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Steam Radiator Air Vent connection size

ocean123 Member Posts: 11
Hello, I have a single-pipe steam system.

I need to replace the air vents on all of the radiators. (The radiators are only warming up halfway.)

How can I determine what size radiator air vents to purchase?

Attached is a picture of the original radiator air vent. I am assuming these are very old. The brand is "Dole".

The male connection piece measures 3/8". The port hole in the radiator also measures 3/8".

However I can't seem to locate any air vents that are that size. All of them are either 1/2" or 1/8" or 3/4".

How can I determine what connection size air vent to purchase?

Thank you!


  • Sailah
    Sailah Member Posts: 826
    That's 1/8" NPT, so order 1/8" vents you'll be fine.
    Peter Owens
  • ocean123
    ocean123 Member Posts: 11
    Thank you! I have ordered a Gorton #4 1/8" vent and will order more if that works. BTW What is 1/8" referring to, if the port measures 3/8"? Perhaps I measured wrong. Thanks!
  • Pipe sizes are based on the internal diameter of the pipe, (ID), so with the wall thickness, the tapping is 3/8's.
    You would be better off to check your main vents on the steam pipes downstairs, as the radiator vents are not big enough to let the air out of all the pipes.
    In that case, you would have large capacity main vents, and smaller radiator vents,( which you already have).--NBC
  • Fred
    Fred Member Posts: 8,541
    Also, be aware that radiators may not heat all the way across during each heating cycle. depending on how cold it is outside and how long the boiler runs during a heating cycle. The goal of balancing radiators and venting them is to make the temp in the room comfortable, not to make each radiator hot all the way across.